Backlight bleed test
A pure black field, plus the near-black levels that tell you whether you are looking at bleed, glow or crushed blacks.
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Code value 0. The field where bleed and glow show.
How to run this test
- Dim the room, but do not switch the lights off completely. A pitch-dark room makes every panel look faulty.
- Set your display to the brightness you normally use. Testing at maximum brightness exaggerates everything.
- Go full screen on the pure black field and give your eyes at least thirty seconds to adjust.
- Sit straight on at your normal distance. Check each corner, then each edge, then the middle.
- Move your head slowly from side to side. Light that follows you is IPS glow. Light that stays put is backlight bleed.
- Photograph it only if you need evidence for a return, and say in the message what the room lighting and exposure were.
What a problem looks like
- Backlight bleed
- Pale patches or bright seams, usually at an edge or corner and pointing inwards, caused by light escaping around the edge of the LCD panel. It does not move when you move your head. Small amounts are normal on almost every LCD. A bright wash across a large part of the screen is not.
- IPS glow
- A silvery or warm sheen across the corners that changes as you move your head and fades when you look at it straight on. It is an inherent property of how IPS panels pass light at an angle, not a defect, and every IPS panel has it to some degree. It is also the single most common reason people return a perfectly healthy monitor.
- Clouding
- Irregular blotches in the middle of the panel rather than at the edges, looking like clouds seen from above. Usually caused by uneven pressure in the panel stack, and it sometimes appears after shipping. More noticeable in dark scenes than in ordinary use.
- A bright line or a lit edge strip
- A hard-edged bright line along one side, rather than a soft gradient, points at a seated panel or diffuser problem rather than ordinary bleed. This is worth returning, because it does not settle down with use.
- Nothing at all, on an OLED
- Expected. An OLED switches its black pixels off entirely, so there is no backlight to leak. If you are on an OLED and see nothing here, the test has done its job.
What to do next
If something looks wrong, check it again in a normally lit room and from straight on, then check whether it appears on a second device. If it only happens on this screen and you are still inside the return window, that is the time to contact the retailer.
Questions people actually ask
How much backlight bleed is normal?
Some bleed is present on the large majority of LCD panels, and thin-bezel designs tend to show more. The practical test is whether you notice it in real content at your normal brightness in a normally lit room. If you only see it on a pure black field in a dark room, it is within what the technology does.
What is the difference between backlight bleed and IPS glow?
Bleed is light physically escaping around the edge of the panel and stays in place when you move. Glow is an angular effect of IPS panels that shifts and fades as you move your head. Bleed is a manufacturing variance; glow is inherent to the panel type and cannot be fixed.
Can backlight bleed get better over time?
Sometimes, slightly. Mild bleed occasionally settles in the first weeks as the panel and frame relax, particularly after shipping in cold weather. Do not count on it, and do not let it push you past your return window.
Does testing in a completely dark room give a truer result?
No, it gives a harsher one. Your pupils open in the dark, which makes any leakage far more obvious than it will ever be in use. Judge the display in the conditions you will actually use it in.
Should I press on the bezel to fix it?
No. Applying pressure to a panel can create permanent marks or new dead areas and will void most warranties. If the bleed is bad enough to bother you, return the unit rather than trying to reseat it yourself.